1. Field of the Invention
The present invention relates to a method of determining an exposure amount and a method of extracting a figure, and more particularly to a method of determining an exposure amount by deciding a region corresponding to the face of a human figure which is present in an original image and determining an exposure amount such that the decided region is printed in an appropriate color, and to a method of extracting a figure so as to extract from an image a region in which a figure to be extracted is present.
2. Description of the Related Art
The portion which attracts the most attention of viewers when appreciating a portrait photograph is the face of the human figure. Therefore, when an original image of a human figure recorded on a film or the like is printed onto a photographic printing paper or the like, it is necessary to determine an exposure amount such that the color of the face of the human figure is printed in an appropriate color.
For this reason, in Japanese Patent Application Laid-Open No. 80242/1988 the present applicant has proposed the following method of determining an exposure amount: On the basis of the experiential rule that a portrait photograph has a high probability of a human figure being located in a substantially central portion of the image, the film image is divided into a plurality of regions which are predetermined in a fixed manner, and each region is weighted so that the weight of the region located in a substantially central portion of the image becomes heavy. A weighted mean value of the densities of three colors in each region is calculated, and an exposure amount is determined on the basis of the weighted mean value. With this method, there has been a problem in that although if the human figure is actually located in the vicinity of the substantially central portion of the image, it is possible to obtain an exposure amount for printing the human figure in an appropriate color, if the human figure is located at a position far removed from the central portion of the image, it is impossible to obtain an appropriate exposure amount.
In addition, the present applicant has proposed the following technique (refer to Japanese Patent Laid-Open No. 346332/1992): A color original image is divided into a multiplicity of pixels, and each pixel is separated into three colors and is photometrically measured. A histogram concerning hue values (and saturation values) is prepared on the basis of the data obtained by photometry, and the histogram thus prepared is divided into the respective rectangles. A determination is made as to which of the divided rectangles the pixels belong, so as to classify the pixels into groups corresponding to the divided rectangles. The color original image is divided into a plurality of regions for each group (so-called clustering), a region corresponding to the face of a human figure among the plurality of regions is estimated, and an exposure amount is determined on the basis of the photometric data of the estimated region.
Further, Japanese Patent Laid-Open No. 160993/1994 discloses techniques in which, in order to improve the accuracy of extracting a region corresponding to the face of a human figure, a region contiguous to outer edges of the image is determined as being a background region, and is excluded, and an extracted region is formed as line graphics, and a determination is made as to whether or not the extracted region is a region corresponding to the face of a human figure, on the basis of the shape of a neighboring region located in the vicinity of the extracted region as well as the shape of the extracted region.
With the above-described techniques, however, if a skin-colored region, such as the ground and the trunk of a tree, is present in the original image, and the hue and saturation of the skin-colored region are similar to the hue and saturation of the region corresponding to the face of the human figure in the original image, there is a possibility of such a skin-colored region being erroneously determined as being a region corresponding to the face of a human figure. In addition, if this skin-colored region is contiguous to a region corresponding to the face of a human figure, the skin-colored region cannot be separated from the region corresponding to the face of a human figure, thereby making it impossible to separate the original image into proper ranges of regions. With the above-described prior art, there has been a problem in that since processing is carried out on the premise that one of the divided regions is a region corresponding to the face of a human figure, if the original image cannot be divided into proper ranges of regions, the region corresponding to the face of a human figure is erroneously determined, thereby making it impossible to obtain an exposure amount for printing the face of the human figure appropriately.
Further, the above-described problem of the erroneous determination of the region to be extracted in the event that the original image cannot be divided into proper ranges of regions applies not only to the extraction of the region corresponding to the face of a human figure, but also to the case in which a region where a particular figure is present is extracted from the image. In other words, there has been a problem in that even if the color and the like of a particular figure to be extracted are known in advance, the region where the particular figure is present cannot be extracted properly in cases where a region whose hue and saturation are similar to those of the particular figure is present in the image, or such a region is contiguous to a region corresponding to the particular figure.